This invention is related to the removal of acid gases from a feed gas. More particularly the invention relates to acid gas removal from high carbon dioxide and hydrogen sulfide containing feed gases. A process is provided for reduced energy requirements in the regeneration of the solvent used to remove the acid gases.
Absorption systems are commonly used for the removal of CO2 from natural gas or synthesis gas. A physical solvent such as a dimethylether of polyethylene glycol (DMPEG) can be used to wash out carbon dioxide and other acid gases such as hydrogen sulfide and carbonyl sulfide. DMPEG solvents are used in systems licensed by UOP LLC under the trademark Selexol™. Cryogenic methanol systems are also known to those skilled in the art for this use including the Rectisol™ process currently licensed by Lurgi AG. Other physical solvents that may be used include a mixture of N-formyl and N-acetyl morpholine, N-methyl-2-pyrrolidone and sulfolane.
After absorption of carbon dioxide and/or hydrogen sulfide and/or carbonyl sulfide by a physical solvent, the solution is regenerated to remove absorbed gases. The regenerated physical solvent can then be recycled for further absorption. Absorption and regeneration are usually carried out in different columns or drums containing packing or bubble cap tray for efficient operation. Regeneration is generally achieved in two stages. First, the absorbent solution's pressure is reduced so that absorbed carbon dioxide is vaporized from the solution in one or more flash vessels, sometimes terminating with a vacuum flash drum. Next, if thermal regeneration is required, the flashed absorbent is stripped with steam in a stripping regenerating column to remove residual absorbed carbon dioxide. Low carbon dioxide levels are needed in order to achieve the required carbon dioxide specifications for treated gas.
The prior art processes have significant power requirements. The solvent processes employ pressures that range from about 2758 to 7584 kPa (400 to 1100 psia) and solvent flow rates that range from 3000 to 20000 gpm. Some of the energy is recoverable from the solvent during pressure let down via turbines. However, conventional turbines have been found to be unreliable and cost prohibitive. The release of relatively large amounts of vapor combined with the high solvent flow rates often means that two or more conventional turbines are required to adequately recover the pump energy. However, the capital costs associated with multiple turbines usually makes this option economically unattractive.
It has now been found that a hydraulic turbocharger can be used to recover energy at a relatively low cost compared to turbines